The present invention concerns improvements in a silicone catheter, a tubular medical device for insertion into the body for the purpose of injecting or withdrawing fluids. Although the invention is described in the following specification with particular reference to a Foley catheter for insertion in the urethra, the invention is equally applicable to similarly constructed medical devices such as endotracheal tubes, tracheal tubes, Dennis tubes (used for decompressing the intestinal tract prior to or after gastrointestinal surgery), rectal catheters, Trocar catheters, hematuria balloon cateters, heart catheters, and others. In addition, the concepts of this invention could also be applied to similarly constructed non-medical devices.
The typical Foley catheter consists of a tube or shaft containing a primary lumen which is the conduit for removal or insertion of the appropriate fluid. Within this primary lumen and attached to the wall thereof is at least one secondary, smaller lumen which is the conduit for the injection of an appropriate gas or fluid for inflation of a balloon anchoring the catheter inside the patient. The anchoring balloon generally consists of a thin, elastic material extending around the exterior of the catheter near its tip and attached at its edges or shoulders to the exterior of the catheter. A hole in the tube wall permits the inflation gas or fluid to enter underneath the elastic material and expand it to a balloon-like configuration.
In use the catheter is inserted into the body cavity, and an inflation fluid is pumped through the secondary lumen to expand the anchoring balloon. This prevents accidental removal of the catheter from the patient and stations the catheter in the appropriate position for efficient use. Once the catheter is so anchored, body fluids can be drained or therapeutic fluids can be injected into the body through the primary lumen. When the catheter is no longer needed, the inflation balloon is deflated by releasing the inflation fluid or gas and the catheter is withdrawn from the body.
Although this basic design for a catheter has been used for a number of years, serious problems remain in the design and method of construction of these devices. In particular, there are problems with the previous methods which have been used to provide the elastic exterior portion which forms the anchoring bubble. For example, in U.S. Pat. No. 3,734,100 issued to Walker et al, a catheter construction is described in which a separate cuff portion is glued at its shoulders to the surface of the catheter. Although the patent illustrates the exterior surface of the catheter as being smooth and regular, unfortunately, in practice the thickness of the cuff portion and the effects of the glue cause surface irregularities at the cuff's shoulders. Thus, in a typical catheter produced by the process of Walker et al. the shoulders of the cuff will protrude beyond the remaining exterior surface of the catheter. This situation is undesirable because such irregularities impede the insertion or withdrawal of the catheter and increase the discomfort to the patient. In addition, such a catheter construction is generally not amenable to mechanized production, and manufacture of the catheters by hand causes additional imperfections and defects.
As an alternative, it has been suggested to cover the exterior of the catheter tube in the area underlying the bubble with a masking (release) material, coating the tip of the catheter including the bubble region with a flexible, inflatable material, and subsequently removing the underlying masking material. For example, in the patents to Harautuneian (U.S. Pat. No. 3,292,627 and 3,304,353) the use of a water soluble masking material is suggested. However, there are several problems with this design. First, in simultaneously removing the water soluble release material and inflating the anchoring bubble, difficulties in the dissolution of the release material frequently cause particles to become lodged in the inflation lumen preventing further expansion of the anchoring bubble. Similarly, as discussed in Harautuneian's U.S. Pat. No. 3,452,756, the masking layer may only dissolve in the localized area adjacent the hole to the inflation lumen. Thus, the anchoring bubble may expand preferentially in that area and cause localized pressure injurious to the body tissue. The same general type of system is shown in British Pat. No. 1,234,037--Steer et al.
Alternatively, U.S. Pat. No. 3,544,668 issued to Dereniuk illustrates the use of a gel as a masking layer beneath the anchoring balloon. Following the formation of the outer skin on the catheter, the gel layer is volatilized by heat. This method is difficult to practice because the outer covering of the catheter must be applied before the release coating has dried or is touched.
A further difficulty encountered with the prior art processes for manufacturing a catheter is that they are not applicable to the most useful catheter material, silicone. It has been found that silicone is more compatible with human tissue than previously used rubber and plastic materials and that the incidence of infection in the body tissues is appreciably reduced with silicone catheters. Although attempts have been made to apply silicone coatings over conventional catheter tube materials, silicone bonds poorly with the majority of these other materials. Accordingly, it is preferable to construct the entire catheter of silicone. Because of silicone's hydrophobic nature, however, it is difficult to apply coatings such as those in the Harautuneian and Dereniuk patents to silicone. Thus, in addition to the problems generally encountered with water soluble or volatile release coatings, a further defect is that these coatings are not useful in preparing silicone catheters.
In view of the foregoing, it is an object of the present invention to provide an improved catheter construction.
It is also an object of this invention to provide an improved silicone catheter and made entirely of silicone.
It is a further object of this invention to provide a catheter which does not suffer the defects of localized swelling of the anchoring bubble or the plugging of the inflation lumen caused by the particles from the release coating.